In lithography techniques, for example, a resist film composed of a resist material is formed on a substrate, and the resist film is subjected to selective exposure of radial rays such as light or electron beam through a mask having a predetermined pattern, followed by development, thereby forming a resist pattern having a predetermined shape on the resist film.
A resist material in which the exposed portions become soluble in a developing solution is called a positive-type, and a resist material in which the exposed portions become insoluble in a developing solution is called a negative-type.
In recent years, in the production of semiconductor elements and liquid crystal display elements, advances in lithography techniques have lead to rapid progress in the field of pattern miniaturization.
Typically, these miniaturization techniques involve shortening the wavelength of the exposure light source. Conventionally, ultraviolet radiation typified by g-line and i-line radiation has been used, but nowadays KrF excimer lasers and ArF excimer lasers are now starting to be introduced in mass production. Furthermore, research is also being conducted into lithography techniques that use exposure light source having a wavelength shorter than these excimer lasers, such as F2 excimer lasers, electron beam, extreme ultraviolet radiation (EUV), and X ray.
Resist materials for use with these types of exposure light sources require lithography properties such as a high resolution capable of reproducing patterns of minute dimensions, and a high level of sensitivity to these types of exposure light sources.
As a resist material which satisfies these conditions, a chemically amplified resist composition is used, which includes a base component that exhibits changed solubility in an alkali developing solution under the action of acid and an acid generator that generates acid upon exposure.
For example, a chemically amplified positive resist composition typically contains a resin component (base resin) that exhibits increased solubility in an alkali developing solution under the action of acid, and an acid generator component. If the resist film formed using this resist composition is selectively exposed during formation of a resist pattern, then acid is generated from the acid generator within the exposed portions, and the action of this acid causes an increase in the solubility of the resin component in an alkali developing solution, making the exposed portions soluble in the alkali developing solution.
Currently, resins that contain structural units derived from (meth)acrylate esters within the main chain (acrylic resins) are widely used as base resins for resists that use ArF excimer laser lithography or the like, as they exhibit excellent transparency in the vicinity of 193 nm (for example, see Patent Document 1). Here, the term “(meth)acrylic acid” is a generic term that includes either or both of acrylic acid having a hydrogen atom bonded to the α-position and methacrylic acid having a methyl group bonded to the α-position. The term “(meth)acrylate ester” is a generic term that includes either or both of the acrylate ester having a hydrogen atom bonded to the α-position and the methacrylate ester having a methyl group bonded to the α-position. The term “(meth)acrylate” is a generic term that includes either or both of the acrylate having a hydrogen atom bonded to the α-position and the methacrylate having a methyl group bonded to the α-position.
On the other hand, a multitude of compounds have been proposed for use as the acid generator in a chemically amplified resist, and known examples include onium salt-based acid generators such as iodonium salts and sulfonium salts, oxime sulfonate-based acid generators, diazomethane-based acid generators, nitrobenzylsulfonate-based acid generators, iminosulfonate-based acid generators, and disulfone-based acid generators.
Currently, onium salt-based acid generators having a cation moiety such as a triphenylsulfonium ion are widely used as the acid generator (for example, see Patent Document 2).
Further, onium salt-based acid generators such as those disclosed in Patent Document 3 are also available, although further improvements are required to achieve better lithography properties.
Furthermore, currently, a nitrogen-containing organic compound such as an alkylamine or alkyl alcohol amine is frequently added to a chemically amplified resist in addition to the base resin and the acid generator (for example, see Patent Documents 4 and 5). These nitrogen-containing organic compounds function as quenchers that trap the acid generated from the acid generator, and contribute to an improvement in lithography properties such as the resist pattern shape. Further, these nitrogen-containing organic compounds also suppress the effects that basic compounds within the air can have on the resist composition, thereby improving the resistance of the composition to Post Exposure Delay (PED).